Conventional pumping units are often inadequate to pump materials having a high density or high solid content. For example, during drilling operation it is common to cool and clean the drill bit with circulating drilling mud. The mud is circulated by pumps which must operate continuously despite the large content of impurities in the mud and its high density. Other applications may require the pumping of solid materials which may flow in a fluid like manner, such as concrete wheat and coal.
In the past, attempts have been made to employ a pumping unit incorporating a flexible bladder positioned within a pumping chamber. The bladder is reciprocated between the walls of the chamber by a crank shaft operating through a connecting rod. The bladder divides the pumping chamber into at least one compartment. The volume of the compartment varies as the bladder is reciprocated and may be employed to impart a driving or pumping force to material entered into the compartment. This apparatus has a number of shortcomings. The bladder is exposed to the pumping pressure on one side thereof while the opposite side is typically open to atmospheric pressure. The pumping pressure is therefore limited by the strength of the bladder. The pressure limit imposed by the present bladder material is significantly less than that necessary for use as a drilling mud pump.
Conventional pumping units which rely on close tolerances between a moving piston and cylinder wall are inadequate for these types of materials. While they may provide sufficient pressure to operate in an environment such as drilling mud circulation, the abrasiveness of the pumped materials rapidly degrades the surfaces in the unit to destroy the necessary seals.
Therefore, a need exists for a pump which will operate to pump high density fluids or fluid solids mixtures which may operate at high pumping pressures. In the particular application of pumping drilling mud, a large volume of output is also required.